Clearance rate of luteinizing hormone and follicle stimulating hormone from peripheral circulation in the pig.

Passive immunization of chronically ovariectomized gilts against gonadotropin releasing hormone (GnRH) resulted in an abrupt cessation of pulsatile secretion of luteinizing hormone (LH) accompanied by clearance from serum with a mean half-life of 30.9 +/- 2.3 (mean +/- SE) and 918 +/- 200 min for the first and second compartment, respectively. Serum follicle stimulating hormone (FSH) was unaffected immediately by passive immunization against GnRH and declined slowly with a half-life of 4.9 +/- .7 d. After LH and FSH had declined to basal levels in passively immunized gilts, injection of a bolus of LH and FSH resulted in peak values within 5 min and depletion curves with half-lives for the first compartment of 28.0 +/- 1.3 and 36.4 +/- 2.6 min and for the second compartment of 679 +/- 98 and 1,230 +/- 54 min, for LH and FSH respectively. These results show that the half-life of LH is similar following immunoneutralization of GnRH or administration of a bolus of LH in immunized gilts and a difference in clearance rates of LH and FSH after initial passive immunization. These results suggest that secretion of FSH in the ovariectomized gilt is controlled by factors in addition to hypothalamic GnRH.